The invention relates to systems for automatically transporting and positioning work pieces for processing at processing stations, particularly to systems for automatically transporting and positioning planar or disk-shaped work pieces at processing stations, and more particularly to systems for automatically transporting and precisely positioning disk-shaped substrates such as a semiconductor wafers at multiple exposure stations.
In the production of certain articles (e.g., semiconductor devices), the associated work pieces must be precisely positioned with respect to the processing apparatus (e.g., a projection mask exposure apparatus). Further, the production of certain articles may involve sequential processing of work pieces at multiple processing stations. The work pieces may be transported between stations, either manually or using an automated transport device. For certain precision processing, it may require that the work piece be precisely positioned with respect to the processing apparatus at each processing station.
Certain transport systems typically move the work piece to different processing locations, and if a precision alignment is required, the work piece is realized. Depending on the precision required, this realignment may take time and involve costly apparatus. Other transport systems mount the work piece on a precision stage system and transport the work piece to various process locations on the precision stage. This technique requires a long stroke, precision stage, which is generally more expensive than a short-stroke stage.
While automated transport devices provide repeatable, systematic results (as compared to manual transports that inevitably involve some human errors), they typically include a complex structure of precision electro-mechanical components. In order to achieve a marginal improvement in the precision of an automatic transport device, significant development efforts and costs are required.
It is therefore desirable to develop a work piece transport system that generally is simple in structure and yet capable of positioning work pieces with high precision, and that more specifically uses an imprecise low-cost stage to move a work piece attached to a chuck or work piece holder and a registration method to precisely and repeatedly locate the chuck and work piece at multiple locations.
The invention provides a system and method for automatically transporting and precisely positioning a work piece at a station for processing. A relatively low precision transport mechanism is utilized to transfer a chuck that holds the work piece to and from the processing station. According to one embodiment of the invention, notwithstanding the use of the low precision transport mechanism, the chuck can be precisely positioned at the processing station by utilizing a quasi-kinematic coupling. More specifically, the chuck is precisely located at the coupling by engaging pre-defined indexing notches at the coupling. In the illustrated embodiment, the chuck is securely held against the coupling at the processing station by suction. The coupling may be supported on a precision stage, which is configured to further position the chuck with the work piece thereon with high precision for processing at the processing station.
In another aspect of the invention, the chuck is configured to securely hold a smooth surface of the work piece by suction. In the illustrated embodiment, the chuck is configured to securely hold a planar substrate. The chuck may be configured to hold work pieces of other configurations without departing from the scope and spirit of the invention.
In a further aspect of the invention, the transport mechanism may be configured to transfer the chuck between multiple processing stations. Each processing station has a similar quasi-kinetic coupling. The coupling may be supported on a single precision stage, which further positions the chuck with relatively high precision with respect to the processing apparatus.
In a further aspect of the invention, the processing stations are projection exposure stations in connection with wafer processing. The wafer is securely held on the chuck by suction. The transport mechanism moves the chuck from one exposure station to another to subject the wafer to a desired exposure sequence.